O LORD God of hosts, who is mighty as you are, O LORD, with your faithfulness all around you? You rule the raging of the sea; when its waves rise, you still them. You crushed Rahab like a carcass; you scattered your enemies with your mighty arm. The heavens are yours; the earth also is yours; the world and all that is in it, you have founded them. —Psalm 89:8–11
The steadfast love and faithfulness of God’s covenant is sure to endure forever because the might of God lies behind it. That might is spoken of here using the most striking of metaphors. In order to grasp it, it may be helpful to take an inventory of all the elements laid before us. We have sea, heaven, and earth, that is, we have creation as a noun. We also have creation as a verb, as an act. And then there is the might of God and the defeat of his enemies. But most uniquely, we have Rahab. The might of God that lies behind his forever steadfast love is that which crushes Rahab. Surely this doesn’t mean crushing a Canaanite woman. What is Rahab here?
Awake, awake, put on strength, O arm of the LORD; awake, as in days of old, the generations of long ago. Was it not you who cut Rahab in pieces, who pierced the dragon? Was it not you who dried up the sea, the waters of the great deep, who made the depths of the sea a way for the redeemed to pass over?” —Isaiah 51:9–10; emphasis mine
“The pillars of heaven tremble and are astounded at his rebuke. By his power he stilled the sea; by his understanding he shattered Rahab. By his wind the heavens were made fair; his hand pierced the fleeing serpent” —Job 26:11–13; emphasis mine
This is very similar to the language used of Leviathan in Psalm 74.
“You divided the sea by your might; you broke the heads of the sea monsters on the waters. You crushed the heads of Leviathan; you gave him as food for the creatures of the wilderness. You split open springs and brooks; you dried up ever-flowing streams. Yours is the day, yours also the night; you have established the heavenly lights and the sun. You have fixed all the boundaries of the earth; you have made summer and winter” —Psalm 74:13–17

Piecing our clues together, it appears as though Rahab is a sea dragon, as in the Mesopotamian myths; a creature associated with chaos. For example, Marduk is said to have defeated the primordial sea goddess Tiamat and to have made heaven and earth from the rent carcass. Thus it is that some accuse the Bible of appropriating pagan mythology at this point.
But earlier in Isaiah we read this, “Egypt’s help is worthless and empty; therefore I have called her ‘Rahab who sits still’” (Isaiah 30:7; emphasis mine). Rahab is also clearly a nation in Psalm 87:4.
What are we to make of this? Back up. Take in the big story. When God delivered His people from Egypt in covenant faithfulness he did so with signs and wonders, with a mighty arm judging not only Egypt, but her gods (Exodus 12:12). Egypt is likened to a sea monster of chaos and by defeating her, by crushing the serpent’s head, a people are formed and brought into a land of milk and honey.
Listen to Isaiah 59 again: “Awake, awake, put on strength, O arm of the LORD; awake, as in days of old, the generations of long ago. Was it not you who cut Rahab in pieces, who pierced the dragon? Was it not you who dried up the sea, the waters of the great deep, who made the depths of the sea a way for the redeemed to pass over?” (emphasis mine). At the Red Sea, Rahab was slain. The serpent crushed. The people of God delivered. The chaos stilled.
And here, all this is being reflected on in reference not to God’s covenant faithfulness to Moses, but to David. And of the King the psalmist will soon say, “I will set his hand on the sea and his right hand on the rivers” (89:25). Here is anticipated the serpent-crushing Seed of the woman who calms the chaos of the seas cursed with the serpent. One cannot but think of the Anointed One, the Christ, who after rebuking the tempest on the sea of Galilee then rebuked the Gaderene demoniacs so that the demons went into the pigs who then rushed down a steep bank and into the sea and drowned (Matthew 8).
Behold the Christ, the Son of David whose hand is on the seas and whose foot is on the serpent’s head. At the cross, when it seemed the King was forsaken, it was then that God’s steadfast love and faithfulness were most manifest as it was there, that the pierced foot crushed the dragon’s head.